Interference measuring and mapping method and apparatus for wireless networks using relay stations

ABSTRACT

Interference levels occurring at one or more stations in a wireless network, where each of said one or more stations is a base station or a relay station. The measured interference levels are mapped by building a first matrix including noise plus interference occurring at each of the one or more stations, respectively, and scheduled transmissions at predetermined times by each relay station respectively are mapped by building a second matrix. The first matrix and the second matrix are multiplied in order to determine the noise plus interference impact upon each base station by each relay station so that a network schedule can be generated in order to increase bandwidth efficiency in the network.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.11/777,566, filed Jul. 13, 2007, now U.S. Pat. No. 7,643,429 and isbased on, and claims the benefit of a U.S. Provisional Application No.60/864,491, titled “INTERFERENCE MAPPING PROCEDURE FOR OFDMA NETWORKSUSING RELAY STATIONS”, filed Nov. 6, 2006, inventors Chenxi Zhu, DorinViorel, Jagan Seshadri, Jonathan Agre and Wei-Peng Chen, and which areincorporated herein by reference.

In addition, this application is based on, and claims the benefit of aU.S. Provisional Application No. 60/891,096, titled “INTERFERENCEMAPPING PROCEDURE FOR OFDMA NETWORKS USING RELAY STATIONS”, filed Feb.22, 2007, inventors Chenxi Zhu, Dorin Viorel, Jagan Seshadri, JonathanAgre and Wei-Peng Chen, and which is incorporated herein by reference

BACKGROUND OF THE INVENTION Description of the Related Art

Wireless communication networks have become increasingly popular andgenerally include a base station that provides service to a cell arealocated around the base station. Subscriber stations, including mobilestations (such as cell phones, etc.), are able to communicate with thebase station when they are within the service area (such as the cellarea) of the base station.

Interference among stations in the same or different cells of thenetwork can cause significant problems. The use of relay stations in thenetwork can complicate interference problems.

SUMMARY OF THE INVENTION

Various embodiments of the present invention provide a method andapparatus which (a) measures interference levels occurring at one ormore stations in a cluster of cells in a wireless network, where each ofsaid one or more stations is a base station or a relay station; (b) mapsthe measured interference levels by building a first matrix includingnoise plus interference occurring at each of the one or more stations,respectively; (c) maps scheduled transmissions at predetermined times byeach relay station respectively by building a second matrix; and (d)determines a noise plus interference impact upon each base station byeach relay station by multiplying the first matrix by the second matrixat various points in time.

Various embodiments of the present invention provide a method andapparatus which (a) measures interference levels occurring in one ormore stations in an Institute of Electrical and Electronics Engineers(IEEE) 802.16 Orthogonal Frequency Division Multiple Access (OFDMA)system, each station of said one or more stations being a base stationor a relay station; (b) maps the measured interference levels bybuilding a first matrix including noise plus interference occurring ateach of the one or more stations, respectively; (c) maps scheduledtransmissions at predetermined times by each relay station respectivelyby building a second matrix; and (d) determines a noise plusinterference impact upon each base station by each relay station bymultiplying the first matrix by the second matrix. Thereby, variousembodiments of the present invention are capable of generating a networkschedule, based on the determined noise plus interference impact.

The above embodiments of the present invention are simply examples, andall embodiments of the present invention are not limited to theseexamples or to including all the features described in the Summary ofthe Invention section of this application.

Additional features of the invention will be set forth in part in thedescription which follows, and, in part, will be obvious from thedescription, or may be learned by practice of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an illustration of an example of a “honeycomb” cluster ofcells in a wireless network topology involving base stations and relaystations operating in an OFDMA network under the IEEE 802.16 standard.

FIG. 2 is a flowchart illustrating the method of measuring interferencelevels occurring at one or more stations in a wireless network, mappingthe interference levels and scheduled transmissions at relay stations bybuilding first and second matrices and determining the noise plusinterference impact upon each base station by each relay station,according to embodiments of the present invention.

FIG. 3 is a flowchart illustrating the method of measuring interferencelevels, according to embodiments of the present invention.

FIG. 4 is an example of portions of UL interference sounding patternstransmitted from a plurality of relay stations operating in a cellwithin a cluster of cells.

FIG. 5 is a flowchart illustrating the method of defining anothercluster of cells and repeating the measuring, mapping and determiningprocedures, according to embodiments of the present invention.

FIG. 6 is a diagram showing newly defined honeycomb clusters of cells ina wireless network topology so that all cells are subject to measuring,mapping and determining procedures, according to embodiments of thepresent invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Reference will now be made in detail to the present preferredembodiments of the present invention, examples of which are illustratedin the accompanying drawings, wherein like reference numerals refer tolike elements throughout.

In wireless communication networks, due to such effects as shadowingarising from blockage by buildings and other obstructions betweentransmission/reception antennas, there exist dead zones in whichcommunication with the base station is not possible, despite beingwithin the service area. To combat this problem, in a wireless network,such as for example, an Orthogonal Frequency Division Multiple Access(OFDMA) network, relay stations can be employed for providing enhancedtransmission capabilities by acting as intermediaries between mobilestations operating in the network and the base station. In this manner,a mobile station that is incapable of connecting directly to a basestation within its cell service area may still connect indirectly to thebase station by first communicating with a relay station that does havea direct link, or possibly an indirect link through additional relaystations, to the base station.

A problem arises, however, in that greater levels of interference areproduced in the network with the addition of base and relay stations.Since the increased intranet interference degrades the carrier tointerference-plus-noise ration (CINR) for the impacted links, properlyscheduling the concurrent transmissions to mitigate the interferencelevels impacts directly the quality of service (QoS) on these links.

Therefore, a network entity schedule algorithm can be defined thatminimizes the intranet interference between different stations (eitherbase stations or relay stations) operating within the wireless network(e.g., an OFDMA network), thereby optimizing CINR degradation and thusallowing higher coding rates to be used on the impacted links.

FIG. 1 is an illustration of an example of a “honeycomb” cluster ofcells 100 in a wireless network topology involving base stations andrelay stations operating in an OFDMA network under the IEEE 802.16standard. The cluster of cells 100 includes a plurality of relaystations (RS01-RS21) and a plurality of base stations (BS01-BS07) withinthe cluster of cells 100. This example topology is intended to show asingle possibility of a network cell, and embodiments of the presentinvention are not limited to any particular topology. For example,embodiments of the present invention are not limited to a network withthe specific number of base and/or relay stations in the specificconfiguration shown in FIG. 1, or a honeycomb cluster of cells, or to ahoneycomb having the specific number of cells shown in FIG. 1.

In the specific example in FIG. 1, RS04 is shown transmitting a networkinterference mapping pattern (described in detail below) to all the basestations BS01-BS07, which is used for mapping interference levelsoccurring at various stations. Of course, the transmissions shown inFIG. 1 are merely illustrative examples and the present invention is notlimited to which station or stations transmit and receive the networkinterference mapping pattern or any other transmission.

Various embodiments of the present invention assume a fixed reusepattern. That is, the base stations and relay stations are assumed to bein fixed positions and each transmitter (either a base station or arelay station) transmits with a fixed power assigned by a networkmanagement entity (not depicted). However, the present invention is notlimited to a fixed reuse pattern and it is also not limited to fixedrelay stations.

FIG. 2 is a flowchart illustrating the method of measuring interferencelevels occurring at one or more stations in a wireless network, mappingthe interference levels and scheduled transmissions at relay stations bybuilding first and second matrices and determining the noise plusinterference impact upon each base station by each relay station,according to embodiments of the present invention. Referring now to FIG.2, at operation 200, interference levels occurring at one or morestations in a wireless network are measured, where each of the stationsis either a base station or a relay station. Details of operation 200will be further provided with reference to FIG. 3 below.

Referring now to the interference level measuring operation 200 depictedin FIG. 3, at operation 300 a maintenance mode is scheduled formeasuring the interference levels in the stations. The measuringinterference mode is, for example, a maintenance type of operation, inwhich an implementation-specific network interference mapping pattern istransmitted from a station using, for example, a constant RF power.

Thus, from operation 300, the process moves to operation 310, in whichthe interference mapping pattern is transmitted from a station. As anexample, each relay station within the cluster of cells subject to theinterference measuring transmits within the same uplink (UL) frame, aspecific UL interference pattern based, for example, on a specific ULsounding sequence. Upon receiving the UL interference patterns, allstations within the cluster of cells execute, for example, execute burstnoise power measurements on the received UL interference patterns. Ofcourse, the present invention is not limited to any particular ULinterference pattern based on any specific UL sounding sequence, or tostations executing any particular burst noise power measurements.

One UL sounding burst may contain, for example, 18 subcarriers. Based onthis value, the following maximum number of UL interference soundingpatterns could be used per sector and cell, where the maximal number ofUL interference sounding patterns represents the maximal number of relaystations the algorithm could monitor, and the Average Per Cellrepresents the average number of relay stations that could be monitoredfor a cluster of cells, employing, for example, a relay station UL relayzone of ten symbols, fully allocated for the interference measurement:

512 FFT 1024 FFT 2048 FFT Average Average Average Per Cell Total PerCell Total Per Cell Total PUSC 6 45 15 90 30 180 (Partial Usage ofSubchannels) AMC 2 × 3 7 48 16 96 34 192 (Adaptive Modulation andCoding)

One silence symbol, for example, may follow a one-symbol UL interferencesounding pattern in order to allow non-synchronized power measurements(across different cells). Of course, the present invention is notlimited to any particular measurements being included in the executedburst power measurements.

Referring to FIG. 4, as an example of portions of UL interferencesounding patterns transmitted from a plurality of relay stations, RS k,RS k+1 and RS k+2 represent three different relay stations operating ina cell within a cluster of cells. It is noted that the present inventionis not limited to any specific number of relay stations or base stationswithin a given cell or cluster of cells. At a specific point t₀ , therelay stations begin transmitting respective UL interference soundingpatterns at distinct frequencies. The sounding patterns arenon-overlapping and, within a cluster of cells, each relay station willuse a unique frequency band of 18 consecutive subcarriers, for example.In the example depicted in FIG. 4, each relay station is capable oftransmitting in three frequency segments (a), (b) and (c). In thisexample, each relay station transmits a sounding pattern using adistinct frequency band within frequency segment (a). However, it isnoted that the relay stations are not required to use the same frequencysegment, and each station could transmit the sounding pattern indistinct frequency segments.

In this example, as shown by the pattern generated by RS k, one silencesymbol 20 follows the one-symbol transmission 10 in order to allownon-synchronized power measurements across various cells in the clusterof cells due to propagation time. The present invention is not limitedto any particular number of pairs of symbols 10 and silence symbols 20,and the number of pairs involved could be increased depending on thenumber of relay stations involved in the measurements. Further, the ULinterference pattern described above is only one example, and one orordinary skill in the art would appreciate that various soundingpatterns and methods of transmitting the sounding patterns could beemployed without departing from the principles of the present invention.

Referring back to FIG. 3, from operation 310, the process moves tooperation 320 where the burst power of the transmitted mapping patternis measured. For example, the burst power measurements executed by thestations are implementation specific and could include, for example,Received Signal Strength Indication (RSSI) measurements or, for example,Carrier to Interference Plus Noise Ration (CINR) measurements. Theseburst power measurements are, for example, proportional with theinterference path between stations sending and receiving the ULinterference patterns. It is noted that measuring burst powers may occurat one or more base stations or one or more super-ordinated relaystations.

From operation 320, the process moves to operation 330 where the networkmanagement entity determines interference levels occurring at eachstation based on the measured burst powers. According to variousembodiments of the present invention, the network interference mappingpattern is scheduled, for example, periodically by the networkmanagement entity. Each base station then, for example, averages thereceived burst power measurements from each station and transmits theaveraged measurements to network management entity to generate theinterference matrix. However, the present invention is not limited toperiodic scheduling of network interference mapping, or to anyparticular types of calculations.

Referring back to FIG. 2, from operation 200, the process moves tooperation 210, where the measured interference levels are mapped bybuilding a first matrix including noise plus interference occurring ateach of the one or more stations.

For example, a network management entity (not shown) produces a mappedinterference matrix based, for example, on noise plus interferencemeasurements performed by different stations positioned within a clusterof cells subject to the interference mapping. That is, the interferencematrix includes the noise plus interference generated by each stationupon each other station.

An example interference matrix (INT) shown below maps the noise plusinterference caused by each station upon each other station in thewireless network. As shown in this example, NI_(ij) represents the noise(N) plus interference (I) caused by station “i” upon station “j”. Theeffect is not necessarily symmetrical due to the potential differenttransmission powers of the stations, although it is assumed that eachtransmitter transmits with a fixed power. This example shows a squareY×Y matrix, but the matrix could also be an Y×M matrix.

${INT} = \begin{bmatrix}{NI}_{1,1} & {NI}_{1,2} & {NI}_{1,3} \\{NI}_{2,1} & {NI}_{2,2} & {NI}_{2,3} \\{NI}_{3,1} & {NI}_{3,2} & {NI}_{3,3}\end{bmatrix}$

The present invention is not limited to this specific manner of mappingthe interference levels, and other manners of mapping the interferencelevels can be implemented. More specifically, the present invention isnot limited to the mapping the interference levels by estimation of theinterference matrix as described above.

From operation 210, the process moves to operation 220, where scheduledtransmissions at predetermined times by each relay station respectivelyare mapped by building a second matrix. The predetermined times may bedetermined, for example, by a network management entity.

The second matrix RS(t) includes the relay station scheduledtransmissions denoted by RS_(a,b) at different points in time, where ais the relay station number and b is the time at which the interferencetakes place. An example of matrix RS(t) is shown below:

${{RS}(t)} = \begin{bmatrix}{RS}_{1,{t\; 0}} & {RS}_{2,{t\; 0}} & {RS}_{3,{t\; 0}} \\{RS}_{1,{t\; 1}} & {RS}_{2,{t\; 1}} & {RS}_{3,{t\; 1}} \\{RS}_{1,{t\; 2}} & {RS}_{2,{t\; 2}} & {RS}_{3,{t\; 2}}\end{bmatrix}$

This example shows a square Y×Y matrix, but the matrix could also be anY×M matrix. Further, the present invention is not limited to thisspecific manner of mapping the relay stations, and other manners ofmapping can be implemented within the scope of the present invention.

From operation 220, the process moves to operation 230 where the firstand second matrix are multiplied in order to determine a noise plusinterference impact upon each base station by each relay station atdifferent points in time.

To compute the effect of all relay stations on a given base station at agiven time t, the following equation is performed, where SCH(t)represents the CINR degradation by the relay stations located in thesame cluster of cells upon existing base stations within the samecluster:

SCH(t) = RS(t) * INT,  or: ${{SCH}(t)} = {\begin{bmatrix}{RS}_{1,{t\; 0}} & {RS}_{2,{t\; 0}} & {RS}_{3,{t\; 0}} \\{RS}_{1,{t\; 1}} & {RS}_{2,{t\; 1}} & {RS}_{3,{t\; 1}} \\{RS}_{1,{t\; 2}} & {RS}_{2,{t\; 2}} & {RS}_{3,{t\; 2}}\end{bmatrix}*\begin{bmatrix}{NI}_{1,1} & {NI}_{1,2} & {NI}_{1,3} \\{NI}_{2,1} & {NI}_{2,2} & {NI}_{2,3} \\{NI}_{3,1} & {NI}_{3,2} & {NI}_{3,3}\end{bmatrix}}$

FIG. 5 is a flowchart illustrating the method of defining anothercluster of cells and repeating the measuring, mapping and determiningprocedures, according to embodiments of the present invention. Referringnow to FIG. 5, at operation 400 another cluster of cells within thewireless network is defined. Measuring interference levels only withinthe original cluster of cells, for example a tier 1 cluster of cells,may not be sufficient to properly map all the interference interactionsbetween all stations within the network. That is, interferenceinteractions may appear between the original tier 1 cluster of cellsunder analysis at a given moment and a tier 2 cluster of cells affectinginterference levels at the stations within the tier 1 cluster of cells.

From operation 400, the process moves to operation 410, where themeasuring, mapping by building a first matrix, mapping by building asecond matrix and determining operations (see FIG. 2) are repeated forstations within the tier 2 cluster of cells. As a result, measuring,mapping a determining procedures may be completed for the tier 1+2cluster of cells.

Of course, the process in FIG. 5 is only one example of a processmeasure and map interference levels at all stations in all clusterswithin a wireless network. The present invention is not limited to thespecific example in FIG. 5. For example, the present invention is notlimited to including each of the specific operations in FIG. 5.Moreover, there are many variations of the specific operations in FIG. 5that can be implemented.

After a given period of time determined, for example, by the networkmanagement entity, new tier 1 and tier 2 groups of cells may be defined.For example, FIG. 6 is a diagram showing newly defined honeycombclusters of cells in a wireless network topology so that all cells aresubject to measuring, mapping and determining procedures, according toembodiments of the present invention. This example topology is intendedto show a single possibility of clusters of network cells (i.e.,honeycomb clusters), and embodiments of the present invention are notlimited to any particular topology.

Referring now to FIG. 6, reference numerals 500(a)-500(f) show all thecells in the wireless network with the shaded cluster as the clustersubject to the measuring, mapping and determining procedures at a giventime. As shown in the example of FIG. 6, a tier 1 cluster is defined at500(a) and new clusters are defined sequentially, as shown in 500(b)-500(f). As shown in this example, some cells in a shaded cluster areincluded in the shaded proceeding and/or succeeding cluster, so that thenoise plus function impact upon each station in a cluster by one or morestations in another cluster may be measured.

According to this example, all of the clusters of cells may beefficiently mapped in six frames. Considering, as an example, a frameduration of 5 ms, the total allocated time for a complete tier 1+2interference mapping would be 30 ms. Of course, the present invention isnot limited to a specific frame duration, and the total time could beallocated in six sequential frames or in six separate frames(non-contiguous in time), depending on network congestion. In otherwords, the measurements could be scheduled by the network managemententity periodically during less congested time frames of the network. Inaddition, because one mapping procedure may not be accurate enough, themeasurements may be repeated and averaged over a predetermined timedetermined by the network management entity, for example.

As a further example, the total interference mapping capacity (expressedin total number of mapped relay stations) of the foregoing algorithmwithin 30 ms is given by the following table:

512 FFT 1024 FFT 2048 FFT PUSC 270 540 1080 AMC 2 × 3 288 576 1152

As a result of determining a noise plus interference impact upon eachbase station by each relay station, the network management entitygenerates a network schedule in real time such that the interferencebetween entities (either base stations or relay stations) is mitigated.The bandwidth can be efficiently allocated using, for example, the reusepattern by assigning resources to individual reuse sets including amaximum number of base stations and relay stations, while, for example,maintaining a cumulative transmission level below the predeterminedthreshold interference level

An example of using interference impacts to schedule transmissions canbe found in Provisional Application titled “REUSE PATTERN NETWORKSCHEDULING ALGORITHM FOR OFDMA NETWORKS USING RELAY STATIONS”, U.S. Ser.No. 60/864,498, filed Nov. 6, 2006, inventors Chenxi Zhu, Dorin Viorel,Jagan Seshadri, Jonathan Agre and Wei-Peng Chen, and which isincorporated herein by reference in its entirety, and U.S. UtilityApplication titled “REUSE PATTERN NETWORK SCHEDULING USING INTERFERENCELEVELS”, U.S. Ser. No. 11/777,385, filed Jul. 13, 2007, inventors ChenxiZhu, Dorin Viorel, Jagan Seshadri, Jonathan Agre and Wei-Peng Chen, andwhich is incorporated herein by reference in its entirety. However, thepresent invention is not limited to the methods of generating networkschedules described by the aforementioned provisional and utilityapplications.

Another example of can be found in Provisional Application titled“LOAD-BASED MMR NETWORK SCHEDULING ALGORITHM WITH FREQUENCY REUSE”, U.S.Ser. No. 60/884,464, filed Jan. 11, 2007, inventors Chenxi Zhu, DorinViorel, Jagan Seshadri, Jonathan Agre and Wei-Peng Chen, and which isincorporated herein by reference, and Non-Provisional Application titled“REUSE PATTERN NETWORK SCHEDULING USING LOAD LEVELS”, U.S. Ser. No.11/777,494, filed Jul. 13, 2007, inventors Chenxi Zhu, Dorin Viorel,Jagan Seshadri, Jonathan Agre and Wei-Peng Chen, and which isincorporated herein by reference. However, the present invention is notlimited to the methods of generating network schedules described by theaforementioned provisional and utility applications.

Various embodiments of the present invention provide a method andapparatus which (a) measures interference levels occurring at one ormore stations in a cluster of cells in a wireless network, where each ofsaid one or more stations is a base station or a relay station; (b) mapsthe measured interference levels by building a first matrix includingnoise plus interference occurring at each of the one or more stations,respectively; (c) maps scheduled transmissions at predetermined times byeach relay station respectively by building a second matrix; and (d)determines a noise plus interference impact upon each base station byeach relay station by multiplying the first matrix by the second matrixat various points in time.

Various embodiments of the present invention provide a method andapparatus which (a) measures interference levels occurring in one ormore stations in an Institute of Electrical and Electronics Engineers(IEEE) 802.16 system, each station of said one or more stations being abase station or a relay station; (b) maps the measured interferencelevels by building a first matrix including noise plus interferenceoccurring at each of the one or more stations, respectively; (c) mapsscheduled transmissions at predetermined times by each relay stationrespectively by building a second matrix; and (d) determines a noiseplus interference impact upon each base station by each relay station bymultiplying the first matrix by the second matrix. Thereby, variousembodiments of the present invention are capable of generating a networkschedule, based on the determined noise plus interference impact.

Various embodiments of the present invention are capable of (a)scheduling a maintenance mode; (b) transmitting, from one or morestations, respective network interference mapping patterns; (c)measuring a burst power of each of the transmitted mapping patterns,respectively, upon receiving the transmitted mapping patterns; and (d)determining an interference level occurring at each of the one or morestations transmitting a mapping pattern based on the measured burstpower transmitted by the respective station.

Various embodiments of the present invention provide a method andapparatus which (a) defines another cluster of cells; and (b) repeatsthe measuring, mapping by building a first matrix, mapping building asecond matrix, and determining for one or more stations in the othercluster of cells, where one or more new clusters of cells are definedafter predetermined periods of time, and the measuring, mapping bybuilding a first matrix, mapping building a second matrix, anddetermining are repeated for one or more stations in the one or more newclusters of cells until interference levels occurring at all stations inall cells in the wireless network are measured.

Various embodiments of the present invention are applicable to IEEE802.16 networks, which includes amendments or extensions to IEEE 802.16.However, the present invention is not limited to IEEE 802.16 networks,and is applicable to other types of networks. The IEEE 802.16 standard,including amendments and extensions, is incorporated herein byreference.

Similarly, various embodiments of the present invention are applicableto OFDMA networks. However, the present invention is not limited toOFDMA networks, and is applicable to other types of networks.

Various embodiments of the present invention are described herein withrespect to “mobile” stations that communicate with base stations andrelay stations in a network. However, the present invention is notlimited to networks with “mobile” stations. Instead, a network mighthave many different types of stations, typically referred to as“subscriber” stations, which communicate with base and/or relaystations. A “mobile” station is one type of “subscriber” station.

According to embodiments of the present invention, the above describedmethods, apparatuses and systems can, for example, mitigate the intranetinterference between different stations (either base stations or relaystations) operating within the wireless network (e.g., an OFDMAnetwork), thereby optimizing CINR degradation and thus allowing highercoding rates to be used on the impacted links, and cause a relatedimprovement on the spectral efficiency per link, considering theimprovement in the related bandwidth efficiency.

Although a few preferred embodiments of the present invention have beenshown and described, it would be appreciated by those skilled in the artthat changes may be made in these embodiments without departing from theprinciples and spirit of the invention, the scope of which is defined inthe claims and their equivalents.

1. A method comprising: executing burst power measurements to measureinterference levels occurring at stations in a cluster of cells in awireless network; mapping the measured interference levels by building afirst matrix including noise plus interference occurring at thestations; mapping scheduled transmissions at predetermined times by eachrelay station of the stations by building a second matrix; determining anoise plus interference impact upon each base station of the stations byeach relay station of the stations by multiplying the first matrix bythe second matrix; and generating a network schedule by a networkmanagement entity based on the determined noise plus interferenceimpact.
 2. The method as in claim 1, wherein the network is an Instituteof Electrical and Electronics Engineers (IEEE) 802.16 OrthogonalFrequency Division Multiple Access (OFDM) system.
 3. An apparatuscomprising: means for executing burst power measurements to measureinterference levels occurring at stations in a cluster of cells in awireless network; means for mapping the measured interference levels bybuilding a first matrix including noise plus interference occurring atthe stations; means for mapping scheduled transmissions at predeterminedtimes by each relay station of the stations by building a second matrix;means for determining a noise plus interference impact upon each basestation of the stations by each relay station of the stations bymultiplying the first matrix by the second matrix; and means forgenerating a network schedule by a network management entity based onthe determined noise plus interference impact.
 4. The apparatus as inclaim 3, wherein the network is an Institute of Electrical andElectronics Engineers (IEEE) 802.16 Orthogonal Frequency DivisionMultiple Access (OFDM) system.